1. Field of the Invention
The present invention generally relates to a substrate holder system used during deposition of a metal film on a substrate.
2. Background of the Related Art
Electroplating, previously limited in integrated circuit design to the fabrication of lines on circuit boards, is now used to form interconnect features such as vias, trenches, and electric contact elements on substrates. One feature-fill process that includes electroplating involves initially depositing a non-metallic diffusion barrier layer over the feature surfaces by a process such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or electroless metal deposition. A metallic seed layer is then deposited on the diffusion barrier layer by a process such as PVD, CVD, or electroless metal deposition. A metal film is then deposited by electroplating on the seed layer. Finally, the deposited metal film can be planarized by another process such as chemical mechanical polishing (CMP).
Electroplating, as well as certain other metal deposition processes such as CMP and electroless plating, are wet processes. The electrolyte solution is a liquid that contains chemicals such as copper sulfate that is a source of copper for the plating process. The electrolyte solution used during electroplating can flow to undesirable locations on the substrate, a substrate holder system used to hold the substrate during electroplating, or other robotic or processing equipment. The copper sulfate in the electrolyte solution can dry on a surface of the substrate or processing equipment into crystals, after the substrate is removed from the electrolyte solution. The crystals can contaminate robots and processing equipment, e.g., the substrate holder system, that come into subsequent contact with the substrate or processing equipment. Metal deposits can also form at undesired locations on the substrate, such as on the edge and/or the backsides.
Electroplating cells, in which substrates are typically disposed within during electroplating, contain electrolyte solution. An anode and the seed layer on the substrate are both immersed in the electrolyte solution during plating. The substrate is supported by, e.g., electric contact elements such as a contact ring. Individual electric contact elements are laterally separated from each other around the periphery of a contact ring. Each electric contact element physically contacts a portion of the seed layer. However, it is difficult to provide an effective fluid seal around the individual electric contact elements between the substrate and the contact ring due to the irregular shape and the position of the electric contact element. Electrolyte solution can flow between the substrate, the substrate holder, and a plurality of spaced electric contacts to flow to the edge and the backside of the substrate. The electrolyte solution flowing to the edge and the backside of the substrates leads to possible deposit buildup at these locations that is generally referred to as backside plating.
Backside plating requires post-plating cleaning of the substrate to avoid contamination problems during subsequent processing. A common technique to remove the unwanted deposits involves the application of an etchant or removal agent to selected surfaces of the substrate in, e.g., spin-rinse-dry (SRD) and integrated bead clean (IBC) systems. The thicker the depth of the unwanted deposits, the longer duration is necessary to remove the unwanted deposits in the SRD or IBC systems. Excessive processing, e.g., cleaning and/or etching of the substrates, by present SRD and IBC systems can be expensive since the materials and chemicals used in such systems are often very expensive and the processing time reduces the throughput of substrates through electroplating systems. Minimizing the amount of backside deposition that forms on the substrates is thus desirable.
To limit the amount of undesired deposits and/or chemicals such as copper sulfate crystals that form on the substrate, the substrate is often spun, preferably from between about 0 RPM to about 3000 RPM, after the substrate is removed from the electrolyte solution within the electrolyte cell. The substrate is secured and displaced within a substrate holder assembly portion of the substrate holder system during the spinning operation. The spinning is intended to remove the electrolyte solution from the surfaces of the substrate and the surfaces of the substrate holder assembly that come in contact with the electrolyte solution. Unfortunately, certain surfaces of the substrate holder assembly and/or substrate form fluid traps. These fluid traps retain, and make it difficult to remove, residual electrolyte solution from the substrate and the substrate holder assembly during spinning. Eventually, the electrolyte chemicals, e.g., crystals, retained within the fluid traps build up on the surfaces of the substrate and/or the substrate holder assembly. Any substrates or processing equipment that subsequently come in contact with either the contaminated substrate or substrate holder assembly may, themselves, become contaminated by the residual electrolyte solution and copper sulfate crystals.
In addition, vacuum chucks often are used by robots to load/unload the substrates respectively in/from various cells. Vacuum chucks that are used in electroplating systems typically employ vacuum plates. However, the rigidity and planar configuration of both vacuum plates and substrates limit establishing a flush interface between the mating components if irregular deposits or built-up chemical crystals are present on a chucking surface of a substrate or the vacuum plate. Vacuum leaks often occur if a flush interface has not been established between the vacuum plate and the substrate.
Therefore, there remains a need for an improved method and apparatus that limits the unwanted deposits and chemical buildup on the substrate and the substrate holder assembly. This limiting of unwanted deposits could be accomplished by providing a substrate holder assembly configured to limit the formation of fluid traps after removal of the substrate from the electrolyte solution so that spinning of the substrate and substrate holder assembly results in more efficient removal of the residual electrolyte solution from the substrate and/or the substrate holder assembly.
The invention generally provides an apparatus and associated method that removes electrolyte solution from a substrate. The apparatus comprises a thrust plate formed from a main thrust plate portion and a substrate extension unit. The surfaces of the main thrust plate portion at least partially defines a spin recess. The substrate extension unit can be displaced between a retracted position and an extended position relative to the spin recess. The substrate extension unit is disposed within the spin recess when positioned in the retracted position. The substrate extension unit at least partially extends from within the spin recess when positioned in the extended position. The substrate is processed by immersing at least a portion of the substrate into a wet solution. Following removal of the substrate from the wet solution, the substrate extension unit is displaced into its extended position and the substrate is spun. Extending the substrate extension unit limits the formation of fluid traps within the substrate holder assembly or between the substrate and the substrate holder assembly.